using System;
using System.Collections.Generic;
using gaemstone.Utility;
using static flecs_hub.flecs;

namespace gaemstone.ECS;

public unsafe partial class Universe
{
	private readonly Dictionary<Type, Entity> _lookupByType = new();

	public void AddLookupByType(Type type, Entity entity)
		=> _lookupByType.Add(type, entity);
	public void RemoveLookupByType(Type type)
		{ if (!_lookupByType.Remove(type)) throw new InvalidOperationException(
			$"Lookup for {type} does not exist"); }


	private EntityRef? CreateOrNull(Entity entity)
		=> EntityRef.CreateOrNull(this, entity);

	public EntityRef? Lookup<T>()
		=> Lookup(typeof(T));
	public EntityRef? Lookup(Type type)
		=> Lookup(_lookupByType.GetValueOrDefault(type));

	public EntityRef? Lookup(Entity value)
		=> CreateOrNull(new(ecs_get_alive(this, value)));

	public EntityRef? Lookup(EntityPath path)
		=> Lookup(default, path);
	public EntityRef? Lookup(Entity parent, EntityPath path)
		=> CreateOrNull(EntityPath.Lookup(this, parent, path));
	public EntityRef? LookupSymbol(string symbol)
	{
		using var alloc = TempAllocator.Use();
		return CreateOrNull(new(ecs_lookup_symbol(this, alloc.AllocateCString(symbol), false)));
	}

	public EntityRef LookupOrThrow<T>() => LookupOrThrow(typeof(T));
	public EntityRef LookupOrThrow(Type type) => Lookup(type)
		?? throw new EntityNotFoundException($"Entity of type {type} not found");
	public EntityRef LookupOrThrow(Entity entity) => Lookup(entity)
		?? throw new EntityNotFoundException($"Entity {entity} not alive");
	public EntityRef LookupOrThrow(EntityPath path) => Lookup(default, path)
		?? throw new EntityNotFoundException($"Entity '{path}' not found");
	public EntityRef LookupOrThrow(Entity parent, EntityPath path) => Lookup(parent, path)
		?? throw new EntityNotFoundException($"Child entity of {parent} '{path}' not found");
	public EntityRef LookupSymbolOrThrow(string symbol) => LookupSymbol(symbol)
		?? throw new EntityNotFoundException($"Entity with symbol '{symbol}' not found");


	public class EntityNotFoundException : Exception
		{ public EntityNotFoundException(string message) : base(message) {  } }
}

public static class LookupExtensions
{
	public static EntityRef CreateLookup<T>(this EntityRef entity)
		=> entity.CreateLookup(typeof(T));
	public static EntityRef CreateLookup(this EntityRef entity, Type type)
		{ entity.Universe.AddLookupByType(type, entity); return entity; }
}